Single-capacitor load sensors are generally known in the art. Such single-capacitor load sensors generally include a pair of electrodes that form a capacitor whose capacitance varies according to, among other things, the distance between the electrodes. Thus, compression of an example capacitor structure causes a change in capacitance. The weight placed on the capacitor structure may be determined by measuring the change in capacitance that results from the compression of the capacitor structure.
One drawback to prior capacitive load sensors is that systems that utilize such structures are prone to inaccuracies because of various environmental factors. For example, a change in humidity is known to cause a corresponding change in the dielectric constant of a capacitor. When the dielectric constant of a capacitor changes, the capacitance changes. Thus, a system that uses the capacitor may see different capacitances for the same weight when measured at different times and in environments having different humidities. Problems may arise if the system is not designed to address such variations.
To compensate for different environmental conditions, sensors must be isolated from such environmental conditions, or systems utilizing such sensors must be designed to account for fluctuations in the environment. Both approaches add to the cost of such devices and systems.
Recently, charge transfer sensors have been found to be useful for sensing touch and proximity. Other applications include fill-level sensing, position sensing, material analysis, and various other applications. Generally, a charge transfer sensor includes two capacitors. A first capacitor is charge to a fixed potential, then that charge is transferred to another known capacitor whose capacitance level is then measured. Through controlled switching and measurement of the transferred charge, a change in capacitance at the first capacitor can be measured.
Present charge transfer sensor designs do not appear to be directed to measuring a load, for example, the weight of a person or object. Furthermore, present capacitive load sensors may be expensive or prone to inaccuracies. Therefore, a charge transfer load sensor that addresses the above-identified deficiencies is desirable.